Histologic changes: Another area in the consolidated region shows this rounded structure (arrow). What is it, and what special stain would help to define it? Answer

Clinical summary Image 4

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This is a blood vessel that shows destructive angiitis. The lumen is displaced by eccentric intimal proliferation and inflammation. The palisaded histiocytes and multinucleated giant cells to the right of the arrow and the necrotic PMNs above them indicate that the lesion is a microabscess in the vessel wall. An elastic van Gieson stain would show focal destruction of the elastic tissue of the vessel wall. See below.

Elastic van Gieson stain

This photo of an artery from another patient shows focal destruction of the inner elastic layer and replacement of the medial muscle by loose fibrous tissue. The outer elastic layer is mostly intact but only faintly stained.

Clinical summaryImage 4

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